U.S. patent number 5,209,076 [Application Number 07/894,440] was granted by the patent office on 1993-05-11 for control system for preventing compressor damage in a refrigeration system.
This patent grant is currently assigned to Izon, Inc.. Invention is credited to Michael L. Hobbs, Gary O. Kauffman.
United States Patent |
5,209,076 |
Kauffman , et al. |
May 11, 1993 |
Control system for preventing compressor damage in a refrigeration
system
Abstract
A microprocessor based device which monitors the operation of a
compressor in a refrigeration system and automatically shuts the
compressor down if a monitored condition is abnormal. Sensors in
the refrigeration system sense conditions such as refrigerant
pressure and temperature, superheat, oil pressure and motor current
draw. If a sensed condition is outside of a safety range and
remains there for a time out period, an alarm condition is
indicated and the device generates a alarm signal and shuts down
the compressor. A detachable display module includes a keypad for
carrying out field programming and a LCD screen for displaying the
refrigerant conditions and programming prompts and commands. A rest
button permits resetting twice before a service call is
required.
Inventors: |
Kauffman; Gary O. (Olathe,
KS), Hobbs; Michael L. (Kansas City, MO) |
Assignee: |
Izon, Inc. (Lenexa,
KS)
|
Family
ID: |
25403075 |
Appl.
No.: |
07/894,440 |
Filed: |
June 5, 1992 |
Current U.S.
Class: |
62/126; 62/127;
62/209; 62/228.3 |
Current CPC
Class: |
F25B
49/005 (20130101); F25B 2600/21 (20130101) |
Current International
Class: |
F25B
49/00 (20060101); F25B 041/00 () |
Field of
Search: |
;62/228.1,228.3,126,127,129,158,227,83,208,209 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tanner; Harry B.
Attorney, Agent or Firm: Kokjer, Kircher, Bowman &
Johnson
Claims
Having thus described the invention, what is claimed is:
1. A microprocessor based apparatus for monitoring the operation of
a cooling system which includes a compressor having a suction side
to which refrigerant gas is delivered and a discharge side from
which the refrigerant gas is discharged, said apparatus
comprising:
microprocessor means;
a visual display controlled by said microprocessor means;
means for sensing the superheat condition of the refrigerant gas at
the suction side of the compressor;
means for monitoring additional operating parameters of the cooling
system;
means for entering in said microprocessor means a selected
superheat value indicative of a gaseous state of the
refrigerant;
means associated with said microprocessor means for comparing the
superheat condition sensed by said sensing means with said selected
superheat value and for deactivating the compressor when the
superheat condition sensed by said sensing means drops below said
selected superheat value;
means for displaying on said visual display the superheat condition
sensed by said sensing means and the values of said additional
operating parameters; and
means for providing a printed record of the superheat condition
sensed by said sensing means and the values of said additional
operating parameters.
Description
FIELD OF THE INVENTION
This invention relates generally to cooling systems and more
particularly to a method and apparatus for preventing compressor
damage due to the presence of refrigerant in a liquid or partially
liquid state at the intake of the compressor.
BACKGROUND OF THE INVENTION
In the operation of refrigeration and air conditioning systems, a
cooling effect is provided by the change of state of the
refrigerant from a liquid state to a gaseous state in the
evaporator. The gaseous refrigerant is compressed by a compressor
and is condensed to a liquid state in a condenser before passing
through an expansion valve and being delivered to the evaporator
again.
The compressor is typically an expensive piece of equipment,
especially in the case of a large compressor such as one used in
air conditioning systems for large commercial, industrial or office
buildings. One of the principal causes of compressor damage is a
condition known as "floodback" or "washout" caused by the presence
of undue amounts of liquid refrigerant at the compressor intake.
The liquid refrigerant cannot be compressed, and its presence in
the compressor causes liquid slugging and damage to various
components, including valves and pistons. The liquid refrigerant
also dilutes the lubricating oil in the compressor and washes
lubricant away from the bearings, cylinder walls and other surfaces
that are subjected to high frictional forces. Dilution of the oil
and the increase in friction shortens the life of the compressor.
Compressor break down has serious consequences in that it requires
costly repair or replacement of the compressor, causes
inconvenience and discomfort due to lack of cooling while the
compressor is out of service, and can destroy expensive material in
cases where cooling is needed for a critical industrial or medical
process.
The presence of unduly wet refrigerant at the compressor intake is
caused by a lack of superheat on the suction side of the
compressor. Conversely, if the superheat is excessive, the cooling
effect of the refrigerant on the compressor is reduced. This can
result in overheating of the compressor motor and/or the valves and
high friction areas of the compressor. If the suction pressure is
unduly low, the refrigerant gas is not present in the system in
sufficient amounts to adequately cool the compressor. Adverse
consequences such as overheating of the motor or other parts of the
compressor can result from this condition.
SUMMARY OF THE INVENTION
The present invention has, as its principal goal, the prevention of
compressor damage due to inadequate superheat at the compressor
intake. Another object of the invention is to monitor a wide
variety of operating characteristics of a refrigeration compressor
and to automatically shut off the compressor in the event of
operation under conditions that can damage it.
In accordance with the invention, a microprocessor based monitoring
device makes use of sensors which detect various conditions at
selected locations in a refrigeration system. Pressure and
temperature sensors on the suction side of the compressor provide
information that allows the superheat to be computed. High and low
safety limits for the superheat of the particular refrigerant can
be entered. If the actual superheat falls outside of the programmed
safety range, the compressor is automatically shut off and alarm
signals are generated to indicate the presence of problem
conditions.
Additional sensors monitor conditions such as the compressor
discharge pressure and temperature, motor current draw and oil
pressure. Again, safety limits are entered and the device
automatically shuts down the compressor and provides an alarm
signal if the system is operating outside of a safe operating range
with respect to any of the conditions that are being monitored. In
order to prevent aberrational or transient conditions from shutting
down the compressor, each parameter that is being monitored is
given a time out period during which an abnormal condition must
continue before shut down occurs.
It is an important feature of the invention that the device can be
reset twice after the compressor has been shut down. As a result,
reset is possible following "brownouts" or other external problems
that are not indicative of a problem in the refrigeration system.
However, if the device is reset twice and another automatic shut
down takes place, it is evident that there is a problem that can
cause compressor damage or other adverse consequences to expensive
equipment. Then, a qualified service technician is required to make
a service call so that the problem can be diagnosed and corrected
before the system can be activated again.
The device of the present invention can be incorporated as an
original part of the refrigeration system, it can be added as an
after market item permanently installed on an existing
refrigeration system, or it can be used as a portable service tool
which can be temporarily attached to different refrigeration
systems in order to obtain representative samples of the operating
characteristics. The data can be collected over an extended time
period to indicate any trends that may be present. For example,
each condition can be sensed every ten minutes over a period of
five days, and the data can be presented in the form of a graph or
in any other meaningful format.
Preferably, the device includes a display such as a liquid crystal
display, along with a key pad for entering program commands and
functions and LED indicators for identifying alarm conditions. The
data can be displayed on the LCD screen on the unit, it can be
printed out by a printer, or it can be transmitted via a modem over
telephone lines to allow display on a remote computer screen.
Alternatively, the unit can be programmed to automatically dial a
programmed telephone number in the event of a compressor shut down
so that appropriate personnel are alerted to the problem and can
take whatever corrective action is indicated under the
circumstances.
DESCRIPTION OF THE DRAWINGS
In the accompanying drawings which form a part of the specification
and are to be read in conjunction therewith and in which like
reference numerals are used to indicate like parts in the various
views:
FIG. 1 is a diagrammatic depiction of a refrigeration system which
incorporates a compressor control device constructed in accordance
with a preferred embodiment of the present invention;
FIG. 2 is a block diagram of the pressure control device;
FIG. 3 is a flow chart of the software that is used in the
compressor control device;
FIG. 4 is a flow chart of the software subroutine used to monitor
the current draw of the compressor;
FIG. 5 is a flow chart of the subroutine used to monitor the
pressure on the suction side of the compressor;
FIG. 6 is a flow chart of the subroutine used to monitor the oil
pressure;
FIG. 7 is a flow chart of the subroutine used to monitor the
pressure on the discharge side of the compressor;
FIG. 8 is a flow chart of the subroutine used to monitor the
temperature on the discharge side of the compressor; and
FIG. 9 is a flow chart of the subroutine used to monitor the
superheat on the suction side of the compressor.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings in more detail and initially to FIG.
1, a conventional refrigeration or air conditioning system includes
a compressor 10 which is driven by an electric motor in a
conventional manner. The discharge side of the compressor 10
connects with a discharge line 12 equipped with a pressure gauge 14
and a pressure relief valve 16. The discharge line 12 delivers
gaseous refrigerant to one or more condenser coils 18 in which the
refrigerant is condensed to a liquid state. Downstream from the
condenser coils 18, the liquid refrigerant passes serially through
a drier 20, a sight glass 22, a pair of manually operated valves 24
and a liquid line solenoid valve 26. After passing through an
expansion valve 28, the refrigerant is boiled in an evaporator coil
30. The gaseous refrigerant that is discharged from the evaporator
coil is applied to the suction or intake side of the compressor 10
through a suction line 32 which may be equipped with a pressure
gauge 34 and a manual valve 36. The cooling system is conventional
and makes use of a conventional refrigerant. However, it is to be
understood that the control device of the present invention may be
used with cooling systems that differ from the specific system
depicted in FIG. 1.
In accordance with the present invention, the operation of the
compressor 10 is monitored and controlled by a microprocessor based
control device which is identified by numeral 38 in FIG. 1. The
control device 38 receives inputs from a number of different
sensors which monitor the operating conditions generally associated
with the compressor 10. A temperature sensor 40 is located in the
suction line 32 of the compressor and provides device 38 with
information as to the refrigerant temperature on the suction side
of the compressor. A pressure transducer 42 monitors the pressure
of the refrigerant in the suction line 32 and provides the device
38 with information as to the suction pressure. Another pressure
transducer 44 senses the pressure of the lubricating oil that is
used for lubrication of the compressor 10 and provides oil pressure
information to the device 38. Another pressure transducer 46 senses
the pressure in the compressor discharge line 12 on the high
pressure side of the compressor. Again, this information is
supplied to the device 38 as one of its inputs. The temperature of
the refrigerant in the discharge line 12 is sensed by a temperature
sensor 48 which provides another input to the device 38. The
electric current that is drawn by the motor of the compressor 10
during operation of the compressor is sensed by one or more current
sensors 50 associated with the electrical control panel 52 which
supplies electrical power for operation of the compressor. The
device 38 receives electrical power from the control panel 52
through suitable power connections 54.
Output signals from the device 38 may be applied to a suitable
printer 56 in order to provide a printed record of the information
that is monitored by the device. Another output signal from the
device 38 may be applied to a modem 58 which is used for
communications along telephone lines in a manner that will be
explained more fully.
Referring now more particularly to FIG. 2, the device 38 includes a
conventional microprocessor 60 which receives power from a power
supply 62 connected with the incoming AC power lines. The device 38
may be factory programmed or provided with an optional programming
and display module 64 which permits programming in the field. The
module 64 may be attached to the device through a detachable
connection 65. The module 64 includes a liquid crystal display
screen 66 and a key pad which includes a number of different keys
68. The LCD display 66 has a suitable interface 70 with the
microprocessor 60. Similarly, the key pad has an interface 72 with
the microprocessor. A clock module 74 connects with the
microprocessor 60 through a suitable interface 76. A reset button
78 is provided on the device 38 and permits the device to be reset
twice, as will be explained more fully.
The device 38 is provided with memory circuits which connect with
the microprocessor 60 through a memory interface 80. The memory
circuits include a random access memory (RAM) 82 having a back up
battery 84, a programmable read only memory (PROM) 86, and an
electrically erasable programmable read only memory (EEPROM)
88.
The suction line temperature sensor 40 may be a conventional sensor
which provides one of the inputs to the microprocessor 60 through a
suitable conversion circuit and an analog to digital converter 90.
Sensors 42, 44, 46 and 48 similarly provide inputs to the
microprocessor 60 through conversion circuits and the analog to
digital converter 90. Preferably, the current sensors 50 are three
in number and are provided in the form of transformers for the
three phases of the electric motor that operates the compressor 10.
The current draw for each phase of the motor is applied from the
respective sensors 50 through suitable converter circuits to the
analog to digital converter 90.
Alarm output signals from the microprocessor 60 are provided
through an alarm interface 92 to operate relay circuits 94. The
relay circuits 94 control equipment control circuits 96 which shut
off the compressor 10 and may perform other functions as well. The
relay circuits 94 also control alarm circuits 98 which generate
suitable visual and/or audio alarms when the compressor is shut
off. Preferably, the device 38 is provided with a face panel that
includes a series of LEDs, one indicating when the power for the
unit is on, another indicating a superheat failure condition,
another indicating a high current failure condition, another
indicating a low suction pressure failure condition, another
indicating a high discharge temperature failure condition, another
indicating a high discharge pressure failure condition, another
indicating a low oil pressure failure condition, and the last
indicating that the unit has been reset twice. These LEDs are
controlled by the alarm circuits 98. If desired, the alarm circuits
may energize an audio alarm in the event of a failure
condition.
The device may also include reset, watch dog and brown out circuits
which are identified collectively by numeral 100 and which have a
reset interface 102 with the microprocessor 60. Optional
communications and printer driver circuitry 104 may be provided and
may interface with the microprocessor through a UART chip 106.
Circuitry 104 is used to suitably operate a conventional printer, a
modem attached to telephone lines, or a computer monitor on which
output information from the device is displayed at a remote
location.
FIG. 3 depicts in flow chart from the software for the device 38.
From a start block 108, block 110 is entered to obtain the input
values of the conditions that are being monitored. These include
the suction line temperature sensed by the temperature sensor 40,
the suction pressure sensed by the pressure transducer 42, the oil
pressure sensed by transducer 44, the discharge pressure sensed by
transducer 46, the discharge line temperature sensed by the
temperature sensor 48 and the motor current draw sensed by the
three current sensors 50. In block 112, the input values are stored
in the RAM 82.
If the module 64 is attached to the unit, block 114 is then entered
and the input values which are stored in the RAM 82 are serially
displayed on the LCD display screen 66. In block 116, the
information input on the keys 68 is obtained, and the functions
that are requested are carried out, as will be explained more
fully. If the communications and printer driver circuitry 104 is
provided, block 118 is entered and the input information is printed
by a printer, is displayed on a remote computer screen, or is
transmitted via modem and telephone lines to a remote location.
When block 120 is entered, a suction pressure sub routine is
carried out, as will be explained in more detail. In block 122, a
test is carried out in which the high amperage limit is divided by
8. The high amperage limit may be programmed into the unit at the
factory or programmed in the field through entries on the key pad.
In block 124, a comparison is made as to whether the amperage
measured by the sensors 50 is less than the result of the test
performed in block 122. If the comparison made in block 124
indicates that the amperage that is sensed is less than that
determined by the test, block 126 is entered. In block 126, various
time out periods are set at preprogrammed initial values. For
example, an amperage high limit timer, a superheat start delay
timer, an oil pressure low limit timer, a discharge temperature
high limit timer and a discharge pressure high limit timer are all
set at initial values which are either programmed at the factory or
in the field through entries made on the key pad. From block 126,
block 110 is entered again.
If the comparison made in block 124 indicates that the amperage
that is sensed is not less than the amperage determined by the test
carried out in block 122, blocks 128 and 130 are entered in
succession, and subroutines that will be explained more fully are
carried out. From block 130, block 132 is entered to determine
whether the oil pressure monitoring option has been installed. If
it has, an oil pressure subroutine is carried out in block 134 and
block 136 is entered. If the oil pressure option is not installed,
block 136 is entered directly from block 132.
In block 136, a determination is made as to whether or not the
discharge temperature sensing option has been installed. If it has,
block 138 is entered and a discharge temperature subroutine is
carried out prior to entering block 140. If the discharge
temperature option is not installed block 140 is entered directly
from block 136. In block 140, a determination is made as to whether
the discharge pressure sensing option has been installed. If it
has, block 142 is entered and a discharge pressure subroutine is
carried out prior to entering block 110 again. If the discharge
pressure option is not installed, block 110 is entered directly
from block 140.
FIG. 4 is a flow chart for the subroutine that determines when the
motor current draw is unduly high. A predetermined high limit for
the current draw is established and may be entered in the EEPROM
88. The amperes subroutine which is entered at block 128 involves
comparing in block 144 the amperage sensed by the sensors 50 with
the predetermined high amperage limit. If the amperage is less than
the high limit, block 146 is entered and the high limit timer value
is set to a predetermined initial value. Block 148 is then entered
from block 146. If the amperage that is monitored is not less than
the high limit, block 148 is entered directly from block 144. In
block 148, a determination is made as to whether the time period
established by the high limit timer has elapsed. If it has not, a
return block 150 is entered and a return is made to the main
program. If the high limit timer period has elapsed, block 152 is
entered from block 148 and the high amperage failure flag is set.
From block 152, a failure mode block 154 is entered to indicate
that a failure has occurred.
FIG. 5 is a flow chart for the suction pressure subroutine 120
which determines when the suction pressure is unduly low. In the
initial block 156, the pressure that is sensed by the suction
pressure sensor 42 is compared with a preselected low limit. If the
measured pressure is greater than the low limit, block 158 is
entered and the suction pressure low limit timer is set equal to a
preestablished initial value before block 160 is entered. If the
pressure that is being measured is not greater than the low limit,
block 160 is entered directly from block 156. In block 160, a
determination is made as to whether the time out period has
elapsed. If it has not, a return block 162 is entered and a return
is made to the main program. If the time out period has elapsed,
blocks 164 and 166 are entered in succession to indicate a failure
mode.
FIG. 6 depicts in flow chart for the oil pressure subroutine 134
which determines when the oil pressure for the lubricating oil of
the compressor is unduly low. In block 168, the oil pressure sensed
by sensor 44 is compared with a preestablished low limit. If the
oil pressure is greater than the low limit, block 170 is entered
and the low limit timer for the oil pressure is set to a
preestablished initial value prior to entering block 172. If the
test carried out in block 168 is not met, block 172 is entered
directly from block 168. In block 172, a determination is made as
to whether or not the time out period for the low oil pressure has
elapsed. If it has not, the return block 174 is entered. If the
time period has elapsed, blocks 176 and 178 are entered to indicate
a failure mode.
In FIG. 7, the subroutine 140 for the discharge pressure of the
compressor is depicted. In block 180, the pressure sensed by
pressure transducer 46 is compared with a preestablished high
limit. If the actual pressure is less than the high limit, block
182 is entered and the discharge pressure timing period is set at
its initial value. Block 184 is then entered to test whether or not
the high limit time period has elapsed. If the discharge pressure
is not less than the high limit, block 184 is entered directly from
block 180. In block 184, a test is carried out to determine whether
or not the high limit timer has decremented to zero. If the time
out period has not elapsed, the return block 186 is entered. If the
time out period has elapsed, blocks 188 and 190 are entered to
indicate a failure mode in the discharge pressure condition.
FIG. 8 depicts the subroutine 138 for the discharge temperature. In
block 192, a test is carried out to determine whether the discharge
temperature is less than a preselected high limit. If it is, block
194 is entered to set the discharge temperature high limit timer to
an established initial value prior to entering block 196. If the
high limit for the discharge temperature is exceeded, block 196 is
entered directly from block 192. In block 196, a determination is
made as to whether or not the high limit timer has run out. If it
has not, the return block 198 is entered. If the time period for
the discharge temperature has elapsed, blocks 200 and 202 are
entered to indicate a failure mode in the discharge temperature
condition.
One of the principal functions of the device 38 is to effect
automatic shut down of the compressor 10 in the event that the
suction line 32 contains undue amounts of liquid refrigerant. For
the refrigerants that are commonly used, data exists in the form of
tables indicating at different pressure and temperature conditions
whether or not there is a superheat condition present corresponding
to a fully gaseous state of the refrigerant. These data are entered
into the device in the form of look up tables stored in the PROM
86. Thus, for each combination of suction pressure and temperature
sensed by the temperature sensor 40 and the pressure transducer 42,
the look up tables contain a particular superheat value which is
determined in block 130.
Referring particularly to FIG. 9, block 204 is entered from block
130. A preselected time delay is entered into the program to
provide time for the superheat to achieve a stable or equilibrium
condition after the compressor is turned on. In block 204, a test
is carried out to determine whether the start delay time period has
elapsed. If it has not, block 206 is entered and high and low limit
timers for the superheat are set to their initial value prior to
entering block 208. If the start delay period has elapsed, block
208 is entered directly from block 204. In block 208, the superheat
which is determined from the look up table is compared against a
preestablished high limit value. If the superheat is less than the
high limit value, block 210 is entered and the high limit timer for
the superheat is set at its initial value prior to entering block
212. If the superheat that is measured is not less than the high
limit, block 212 is entered directly from block 208.
In block 212, the superheat that is determined from the look up
tables is compared with a preselected low limit. If the superheat
is greater than the low limit, block 214 is entered and the low
limit timer for the superheat is set at its initial value prior to
entering block 216. If the superheat is not greater than the low
limit, block 216 is entered directly from block 212. In block 216,
a determination is made as to whether the high limit timer for the
superheat has run out. If it has, block 218 is entered and the
superheat failure flag is set prior to entering the failure mode
block 220. If the superheat high limit timer has not run out, block
222 is entered from block 216 to determine whether the low limit
timer for the superheat has run out. If it has, block 218 is
entered from block 222. If it has not, the return block 224 is
entered from block 222.
In operation, the device 38 monitors the various operating
conditions associated with the compressor 10 and acts to provide
the information which is monitored and to automatically shut down
the compressor 10 if the compressor is operating under conditions
that could cause damage to it. If the display module 64 is used,
the device can be programmed in the field through the keys 68 on
the key pad, and the display screen 66 provides various displays.
Normally, the display screen 66 is in a display mode during which
the conditions that are monitored by the various sensors are
serially displayed, with each condition being displayed on the
screen 66 for a selected time period. The key pad preferably
includes one key 68 having an up arrow which can be depressed in
order to achieve a rapid advance through the conditions that are
being monitored. Another of the keys 68 preferably has a down arrow
which can be depressed in the normal display mode in order to
rapidly advance in a reverse order through the display of the
conditions that are being monitored. Another of the keys 68 is
preferably an enter key which can be depressed in the normal
display mode to lock in the display on a particular condition, and
that condition will be continuously updated on the display screen
66. Another of the keys 68 may be a cancel key which can be
depressed to enter the normal display mode again.
The final key 68 may be a function key which can be depressed to
display a function menu on the screen 66. Although various
functions can be included in the function menu, one of them is
preferably a print function. Selection of the print function
initiates operation of a printer that is attached through the
serial communications circuitry 104.
Another available function is a set function. If it is selected,
the display 66 requests entry of a valid pass code. The user must
then enter a valid pass code in order to gain entry to the set
menu. If a valid pass code is not entered with 30 seconds, the unit
automatically reverts to the normal display mode.
In the set function mode, one of the menu options is a time setting
in which the current time and date are entered into the unit.
Another option in the set menu is a scale setting function. In this
mode, the screen 66 displays various questions and prompts asking
the user to enter various types of information such as which of the
optional sensors is installed.
Another of the options available on the set menu is the limit
setting function. In this mode, the user is able to program the
various high and low limits for the different conditions that are
monitored by the device and to program the various time periods
during which the conditions must be out of a safe range before an
alarm condition is recognized. The limits and time out periods are
entered through the key pad and are held in the EEPROM 88. In the
PROM 86, predetermined default values are provided for the safety
limits, calibration parameters and time out periods. If the user
fails to select values for any of these, the default values are
automatically used.
When the compressor 10 is in operation, the sensors monitor the
various conditions of the cooling system and display the monitored
conditions on the LCD screen 66, on a remote monitor through the
serial communications circuitry 104, and/or provide a printed
record of them if a printer is attached. If any one of the
conditions that is being monitored is sensed as being outside of
the established limit or limits, and if it remains outside of the
established limit or limits throughout the duration of the time out
period for that particular condition, then the device enters the
failure mode. Through the alarm interface 92, the relay circuitry
94 is activated and causes the equipment control circuit 96 to
immediately shut off the compressor 10 in order to prevent it from
being damaged. At the same time, the relay circuit 94 activates the
alarm circuits 98 in order to energize the alarm LED associated
with the fault condition. The LED provides a visual indication of
the particular condition that is abnormal (such as an unduly low
suction pressure indicating that insufficient refrigerant is in the
system or an unduly low superheat indicating that too much liquid
refrigerant is present at the suction or intake to the compressor
10). If a modem is present and connected with the microprocessor
through circuit 104, a selected telephone number can be
automatically dialed to provide a telephone message indicating that
the compressor has been shut down because of a fault condition.
Appropriate personnel who are off-site can thus be alerted by
telephone that there is a problem.
The device 38 can be reset and the compressor 10 can be started up
to two times simply by depressing the rest button 78. Thus, if
there is a fault condition due to an external factor such as a
power "brownout" or some other external problem not indicative of a
problem with the refrigeration system, the user can reset the
device. However, if the compressor is shut down by the device after
two resets have been effected, the reset button 78 is thereafter
ineffective and it is necessary for a service technician to make a
service call in order to allow the compressor to be started again.
Therefore, if a problem persists causing the system to shut down
three times, there is a high probability that the refrigeration
system is subject to a problem that could possibly damage the
compressor or other components. Then, the service technician must
inspect the system and take whatever corrective action is required
to allow the system to operate safely and normally.
In this manner, the device 38 monitors the operation of the
compressor 10 and immediately shuts it down if a problem condition
is sensed that could lead to compressor damage. It is particularly
important to monitor the superheat on the suction side of the
compressor to make certain that there is not an undue amount of
liquid refrigerant present that could cause a "wash out" or undue
slugging of the compressor that could have serious adverse
consequences. In addition, by monitoring the suction pressure,
assurance is provided that adequate refrigerant is present in the
system to properly cool the compressor and prevent overheat of the
motor or other important components.
The device 38 is particularly useful in monitoring the operation of
a large compressor of the type used in the air conditioning systems
for large industrial, commercial and office buildings. These
compressors are expensive and it is particularly important to avoid
damage to them. The device 38 is also applicable in cooling
processes that require cooling of expensive materials used in
critical industrial or medical processes.
The device 38 can be provided as an original part of the
refrigeration system or it can be permanently installed as part of
an existing refrigeration system. Alternatively, the device can be
provided as a portable servicing tool which can be temporarily
attached to a refrigeration system in order to monitor its
operation for a preselected time period such as a one or two day
period to determine if there are any operating irregularities. By
providing for the field programming of the limits and time out
periods, users can customize the device in the field to conform
with different types of cooling systems which may require different
limits and time out periods. Consequently, the device is adapted
for use with a wide variety of different types and sizes of
mechanical cooling systems.
From the foregoing, it will be seen that this invention is one well
adapted to attain all the ends and objects hereinabove set forth
together with other advantages which are obvious and which are
inherent to the structure.
It will be understood that certain features and subcombinations are
of utility and may be employed without reference to other features
and subcombinations. This is contemplated by and is within the
scope of the claims.
Since many possible embodiments may be made of the invention
without departing from the scope thereof, it is to be understood
that all matter herein set forth or shown in the accompanying
drawings is to be interpreted as illustrative and not in a limiting
sense.
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